1. Field of the Invention
Gases, such a natural gas, are often analyzed by gas chromatographs. Other chromatographs are used to analyze liquids. Some gases may have entrained liquids that cannot be analyzed by gas chromatographs. One use of the present invention is to separate liquids from gases so the gas can be analyzed by a gas chromatograph.
2. Description of Prior Art
Spot sampling is a procedure that is well known in the natural gas industry and is commonly used. For example, the Gas Processors Association (xe2x80x9cGPAxe2x80x9d) has established standard 2166 for proper spot sampling techniques. Spot samples of natural gas are taken in the field from a pipeline and placed in a sample cylinder. The sample cylinder and the gas sample are then transferred from the field to a laboratory for analysis, frequently by a gas chromatograph. Because gas chromatographs cannot analyze liquids, it is desirable to try and keep liquids out of spot samples or in the alternative, alert the laboratory when unavoidable liquids are encountered so appropriate measures can be taken to safeguard the chromatograph.
Welker Engineering Company of Sugar Land, Tex., the assignee of the present patent application, has previously sold a sight glass without a filter called the model SG3. The SG3 sight glass was primarily used with odorant injection systems to provide visual confirmation that the odorant was being properly injected into the system. The SG3 was also used to provide visual confirmation in other chemical injection systems that used glycol. In some situations, the SG3 has been used at a spot sampling station to visually determine if liquid was being transferred into a sample cylinder. The SG3 did not prevent liquids from entering a sample cylinder.
Welker Engineering Company has also previously sold a filter without a sight glass called the LE2. The LE2 filter has been used at spot sampling stations to keep liquids out of sample cylinders. However, the LE2 did not provide any visual information to the personnel that were taking the spot sample.
Other companies, such as A+ Corporation of Prairieville, Louisiana also sell liquid separators and filters to keep liquids out of sample cylinders at spot sampling stations. Some of these products from A+ are described in the company web site (www.apluscorporation.com). Pages from this web site are included in the Information Disclosure Statement filed concurrently herewith. In summary, the prior art filters and liquid separators from both Welker Engineering Company and A+ Corporation do not incorporate a sight glass. There is a need to incorporate a sight glass with a liquid separator so operators may modify their technique while a spot sample is being taken. Some liquids can be eliminated through the modification of spot sampling techniques; other naturally occurring liquids many be unavoidable and will persist even if the spot sampling techniques are modified.
When a spot sample is being taken, improper technique can lead to the unwanted creation of liquids due to the Joule-Thomson effect. Running natural gas through valves and/or a sample cylinder during a spot sampling operation can create a sharp pressure drop which may chill the gas and lead to condensation of unwanted liquids. If an operator can visually observe that liquids are present, adjustments may be made to the sampling technique that will reduce or eliminate the creation of unwanted liquids. A more representative spot sample will be taken if condensation does not occur during the sampling operation which can lead to creation of unwanted liquids.
However, even if proper techniques are used, some natural gases have entrained liquids that cannot be eliminated by adjusting spot sampling techniques. In these circumstances, it is necessary to have a liquid separator to keep the sample dry for the gas chromatograph. There is a need for a liquid separator that incorporates a sight glass to enhance spot sampling operations.
The present invention is a combination sight glass and liquid separator. The present apparatus may be used at spot sampling stations to adjust technique and eliminate liquids from the sample. The present invention includes a high pressure glass window that allows the apparatus to operate at pressures up to 2,000 psi. An optional protective shield protects the glass window from inadvertent damage. A membrane filter is porous to gas and substantially impermeable to liquids. A polytetrafluoroethylene membrane is positioned on a porous sintered stainless steel support. Other membranes and supports may also be suitable provided they allow the gas to pass and stop the liquids. A drain is positioned in the liquid separator to drain liquids from the apparatus.